When I had a similar problem with a Russian 105 mm lens I bought s set of 39 mm macro extension tubes from one of the FSU sellers on Ebay. They are designed to be used for thread mount Leicas or Leica copies which use the same diameter and thread as most enlarger lenses. IIRC a set of three or four tubes of various lengths cost me less than an extended lens board.

As an added bonus the macro tubes came with instructions, in Russian, on how to take macro pictures with them as well as a table of focus distance and exposure settings.